Effect of Annealing on the Magnetic Properties of FeCoNiCuNbSiB Soft Magnetic Alloys

A series of nanocrystalline soft magnetic alloys with nominal compositions of Fe66.8-xCo10NixCu0.8Nb2.9Si11.5B8 (x = 1–15 at%) were developed and studied. Effects of annealing on the soft magnetic properties, crystallization behavior, and domain structure were investigated. The alloys with higher Ni content were prone to exhibit stronger magnetic anisotropy. The Fe66.8Co10Ni10Cu0.8Nb2.9Si11.5B8 alloy exhibited excellent soft magnetic properties, including the low permeability of 2000, low coercivity of about 0.6 A/m, and low remanence of 2.4 mT, together with a temperature gap of 128 K between two crystallization onset temperatures. It has been found that the Ni content and the annealing process possess significant effects on the soft magnetic property of the nanocrystalline alloys. It shows that the developed Fe66.8Co10Ni10Cu0.8Nb2.9Si11.5B8 nanocrystalline alloy exhibits great potentials for applying in the field of common mode chokes or current transformers, due to its ability to resist the direct current.

Interpretable machine-learning strategy for soft-magnetic property and thermal stability in Fe-based metallic glasses

Fe-based metallic glasses (MGs) have been extensively investigated due to their unique properties, especially the outstanding soft-magnetic properties. However, conventional design of soft-magnetic Fe-based MGs is heavily relied on “trial and error” experiments, and thus difficult to balance the saturation flux density (Bs) and thermal stability due to the strong interplay between the glass formation and magnetic interaction. Herein, we report an eXtreme Gradient Boosting (XGBoost) machine-learning (ML) model for developing advanced Fe-based MGs with a decent combination of Bs and thermal stability. While it is an attempt to apply ML for exploring soft-magnetic property and thermal stability, the developed XGBoost model based on the intrinsic elemental properties (i.e., atomic size and electronegativity) can well predict Bs and Tx (the onset crystallization temperature) with an accuracy of 93.0% and 94.3%, respectively. More importantly, we derived the key features that primarily dictate Bs and Tx of Fe-based MGs from the ML model, which enables the revelation of the physical origins underlying the high Bs and thermal stability. As a proof of concept, several Fe-based MGs with high Tx (>800 K) and high Bs (>1.4 T) were successfully developed in terms of the ML model. This work demonstrates that the XGBoost ML approach is interpretable and feasible in the extraction of decisive parameters for properties of Fe-based magnetic MGs, which might allow us to efficiently design high-performance glassy materials.

Ultrafine FeNi3 Nanocrystals Embedded in 3D Honeycomb-Like Carbon Matrix for High-Performance Microwave Absorption

The reasonable design of magnetic carbon-based composites is of great significance to improving the microwave absorption (MA) performance of the absorber. In this work, ultrafine FeNi3 nanocrystals (5–7 nm) embedded in a 3D honeycomb-like carbon matrix (FeNi3@C) were synthesized via a facile strategy that included a drying and carbonization process. Because of the soft magnetic property of the FeNi3 nanocrystals and their unique 3D honeycomb-like structure, the FeNi3@C composites exhibit excellent MA abilities. When the filler loading ratio of FeNi3@C/paraffin composites is only 30 wt%, the maximum reflection loss (RL) value is −40.6 dB at 10.04 GHz. Meanwhile, an ultra-wide absorption frequency bandwidth of 13.0 GHz (5.0–18.0 GHz over −10 dB) can be obtained in the thickness range of 2.0–4.5 mm, and this means that the absorber can consume 90% of the incident waves. It benefits from the dual loss components, multiple polarizations, and multiple reflections for improving MA performances of FeNi3@C composites. These observations suggest that the 3D honeycomb-like FeNi3@C composites have broad application prospects in exploring new MA materials that have a wide frequency bandwidth and strong absorption.

A Novel Fabrication of Spherical Fe50ni50 Alloy Powders via in-Situ De-Wetting of Liquid Solid Interface

: Spherical Fe50Ni50 alloy powders were fabricated via a novel route based on in-situ interface de-wetting between liquid Fe-Ni alloy and alumina. The obtained Fe50Ni50 alloy particles exhibit very good spherical shape according to SEM images. Furthermore, the cross-sectional SEM images show that there are no pores and bulk inclusions in the internal region of the spherical particles. The XRD results show a trace amount of the impurity alumina phase appearing in taenite phase. The size distribution agreed well with the SEM observation confirms that the alumina powders successfully segregated pre-alloy powders. As an incidental benefit, the surface alumina particles were treated as the electrical insulation coatings. The magnetic character shows that spherical Fe50Ni50 powders exhibit a good soft magnetic property even though with a slightly decreasing of saturation magnetization due to non-magnetic coatings. Our strategies provide a method to in-situ fabricate insulation coated Fe-Ni spherical alloy powders as magnetic powder core.

Soft magnetic Fe5C2–Fe3C@C as an electrocatalyst for the hydrogen evolution reaction

Herein, cubic iron carbide@N-doped carbon core-shell particles exhibited soft magnetic property and efficient HER catalytic activity.